This invention relates to a unique concept and implementation of a technology which allows a set of general purpose, high density, controlled impedance interconnect lines to be completely personalized by forming "spot" links on the top, and only the top, layer of the substrate.
Traditionally, a custom approach has been taken for substrate interconnect design in which each layer in the substrate is custom designed and fabricated for the particular intended application. Recently, the concept of quick turnaround has been introduced into substrate design to minimize the number of custom layers required. In prior arts, quick turnaround substrates have been personalized for each new application by customizing the top few layers using discrete wires or a fabrication process similar to that required for the basic unpersonalized substrate. The disadvantages of the previous approaches are that substrates cannot be stockpiled in completed form, long links are required for final personalization, and expensive processing or clean room facilities are needed.
This invention differs from the U.S. Pat. No. 4,489,364, for example, in two important respects. First, no flywires or discrete jumper wires are required with this invention (i.e., all connections of the present invention are made with spot links), and second, the substrate can be completely personalized with this invention rather than only providing for engineering changes (i.e., much higher interconnect density is allowed). Buried general purpose orthogonal lines were used and the fabrication completed in U.S. Pat. No. 4,458,297 for the quick turnaround substrate, however personalization was accomplished with fusible links. The disadvantage of the latter approach is that either the electrical performance suffers from long stubs remaining in the interconnect networks after personalization or an unacceptable number of fusible links are required for a high density substrate.